This invention relates generally to force sensors and force sensing methods. This invention can be used for sensing pressures and fluid flow frictional forces, for example.
Two physical parameters of importance in the oil and gas industry are pressure and fluid flow friction. Pressure in an oil or gas well is used for analyzing the ability of the well to produce hydrocarbons, for example. Friction of a flowing fluid, such as in a tubular member or string in a well or an annulus thereabout, is used for calculating pressure losses in the tubular string or annulus during treatment processes and during the production phase of the well.
Pressure measurements can be performed in many ways. For high pressure measurements in oil or gas wells, Bourdon tubes, strain gauges, and crystal transducers have been used. Bourdon tubes are typically not accurate as compared to at least some more recent downhole pressure measuring devices. Strain gauge sensors are also not too accurate, but they are widely used because they are relatively inexpensive. Pressure sensors having crystal resonators are highly accurate; however, they are also relatively expensive and temperature sensitive. This latter characteristic can require sophisticated temperature correction schemes. There is the need for a preferably less expensive but accurate force sensor that can sense pressure, particularly high pressure in an oil or gas well, under various temperature conditions.
Friction measurements have been made using friction sensors that are located in a flow line, but these devices typically need to be long if accuracy is needed. Friction measurements have also been empirically made using laboratory data. These empirical measurements are based on values of "n" and "k" developed from laboratory experiments. This type of friction determination can be inaccurate because actual field generated fluids are often different from test fluids created in the lab. Moreover, using n and k values creates computational errors in two ways: converting friction or shear values to n and k values, and then using the n and k values to convert dimensional values to friction or shear values. There is the need for a more compact force sensor that can be located in-line to sense actual frictional forces, even of abrasive and other material-attacking fluids such as are encountered in the oil and gas industry, so that the typically less accurate empirical technique does not have to be used.
There is also the need for a corresponding method for sensing force, such as either pressure or fluid flow friction.